NEW YORK (Reuters Health) - The growing number of hospital-based physicians in the U.S. could be taxing Medicare resources, government-funded researchers suggest in a new report.

They found hospitalized Medicare patients checked out sooner when they were cared for by a hospital doctor than when their primary care physician followed them. Yet they were also more likely to bounce back into the hospital over the next month.

As a consequence, the savings from the shorter original stay were offset by a higher bill for health services later -- potentially adding up to an extra $1.1 billion across all Medicare patients.

Hospital-based doctors, also called hospitalists, have become increasingly common in recent decades, and now tally some 30,000 in the U.S., according to the Society of Hospital Medicine.

The idea behind the movement is to streamline and improve patient care, and earlier research has shown that the approach does indeed lead to shorter hospital stays.

But according to the new report, few studies have followed patients after they are sent back out into the community.

To see what happens to them, Yong-Fang Kuo and Dr. James S. Goodwin from the University of Texas Medical Branch in Galveston studied a national sample of Medicare patients who landed in the hospital between 2001 and 2006.

All of the patients -- some 58,000 -- had a primary care physician before they were admitted, but more than a third of them ended up being cared for by a hospitalist.

As expected, those who were followed by a primary care physician spent about half a day more at the hospital, costing Medicare $282 more on average than patients cared for by a hospitalist.

But in the month following hospital discharge, the spending pattern was turned on its head. Patients who'd been under hospitalist care incurred the most expenses, averaging an extra $332.

Most of that added cost came from readmissions, and another big chunk from patients being sent to nursing homes instead of back home. Overall, 76 percent of patients who were followed by their primary care physician were sent back home after leaving the hospital, compared to less than 71 percent of those managed by a hospitalist.

Broadened out to the quarter of Medicare patients who get hospitalist care, that would mean 120,000 patients discharged to other health care facilities instead of home and $1.1 billion annually in additional spending, Kuo and Goodwin estimate.

"Hospitalists, who typically are employed or subsidized by hospitals, may be more susceptible to behaviors that promote cost shifting," they write in the Annals of Internal Medicine.

But, they add, it's impossible to rule out that unmeasured differences are at play, despite the fact that the study did adjust for various patient and hospital characteristics.

"Kuo and Goodwin's findings remind us that we need more studies that follow our patients wherever they go and help us practice the sort of coordinated care that is most likely to lead to high-quality outcomes," Chen and Sanjay conclude.

Dr. Joseph Li, president of the Society of Hospital Medicine, told Reuters Health the new study is well-done, but has a major drawback.

"It didn't look at the quality of care," he said. "It's really hard to look at cost without looking at quality."

Li said the hospitalist movement has burgeoned in response to a growing pressure on primary care doctors, who may not have time to drop by the hospital before rushing off to the office.

"Our country is trying to figure out now, 'how do we get better value for our money,'" he said. "Ultimately, we want to improve the value of the healthcare that we purchase as consumers."